: Hi, our house is a two story home about three years old. Our problem is in the second floor master bed & bath room. When our master toilet, shower or tub is draining there's a sharp knocking against the sub floor coming from the bed room. The knock is fairly consistent but slow with one coming about every five-ten seconds or so while draining.

: We've lived here for over two years with no problems till now. What could this be and could it be serious? I'm left wondering if this is more of problem with the sub-floor rather than an actual plumbing problem.

Aaron,What you hear, is normal expansion and contraction of the plastic drain pipes. If they are strapped tight, or inserted through crooked holes, they will tend to bind and make more noise. It's a bother to listen to them, but rather harmless.